Return Loss is a useful measure of the reflected power at the junction of a transmission line and terminating impedance. A low (negative dB) value of return loss represents lower reflected (lost) power and higher forward transmission in a communication system.
 
  Since the impedance mismatch is related to the signal frequency, the return loss is a curve of impedance mismatch versus signal frequency.
 
  From the electronic technology point of view, the transmission system in a more serious impedance mismatch state will have two problems: one is that the signal power transmitted from the signal source to the load resistance is reduced, and the second is the generation of reflected waves.
 
  Under the impedance matching condition at either the source or the load, the amplitude of the signal transmission deviates from the standard value of 1/2. And delay the signal transmission time, but the waveform does not diverge
 
  Under the condition of impedance mismatch at both the source and the load, the signal transmission not only deviates from the standard value of 1/2 in amplitude, but also has a jump caused by reflected waves at the initial stage and after the end of the signal. It takes several signal transmission times before the top of the waveform gradually converges to a voltage that deviates from the standard value. After the waveform ends, it also takes several signal transmission times before it returns to the zero line.

  Therefore, under the condition of impedance mismatch (i.e., failure of return loss), it must bring false codes to the data transmission system.